The present invention relates to monitoring or control of work heating temperature in flame hardening, and more particularly to a method making it possible for workers to control positions and moving speed of a torch so that the work heating temperature can be maintained within a predetermined temperature range, by notifying the workers of the change in the work hating temperature.
Flame hardening is a kind of surface hardening method. Flame hardening is performed by introducing a mixture of fuel gas and oxygen at an increased flow rate into a torch, combusting this mixture gas at the nozzle tip of the torch, and rapidly heating the surface layer of a work with a high-temperature flame obtained by the combustion. In flame hardening, heating speed is high and the temperature distribution in a work depicts a gentle curve, so that, in order to achieve an intended hardening temperature at a predetermined depth, the surface temperature of the work needs to be raised considerably high. Because this temperature gradient occurs due to the heat transfer by the heat conduction phenomenon, the measurement of the surface temperature of a work plays an important role. Since the measurement with a thermometer and the setting thereof are difficult because of the high heating speed, the temperature judgment by a visual observation is essential.
Conventionally, for example, the flame hardening of the cutting edge part of die used for press-molding automobile parts has relied on empirical work by the visual observation of skilled workers. However, in recent years, because of the improvement of the quality of products and the shortage of skill workers, the conventional method which has quite relied on skill is raising a problem. That is, in order to improve the quality of products, it is necessary to eliminate variations in the flame hardening hardness to maintain homogeneous cutting edge hardness characteristics, and further to leave the results obtained, as quality data. However, since the flame hardening has been performed in such a manner that a worker moves the torch while observing the color of the steel material of a flame-hardened member, wide variations have occurred in the results depending on personal properties or lighting conditions in the surroundings. Furthermore, since the heating temperature on a work surface cannot be left as calculative data, it has been pointed out that a problem arises in that, when customer-complaint due to poor flame hardening takes place after a product has been shipped, it is impossible to trace and investigate the cause of the poor flame hardening.
In accordance with the method for monitoring a work heating temperature in flame hardening of the present invention, the temperature of the work surface heated by flame poured from the torch for use in flame hardening is measured; the measured value is converted into a physical quantity which appeals to the perception of a worker; the measured value is compared with a predetermined standard temperature range; and a warning signal is produced when the measured value approaches the upper limit or the lower limit of the standard temperature range.
Even this allows a worker to obtain a work environment different from the conventional one, and to work much more easily. In addition, the present invention aims at a further improvement in the accuracy and a superior workability, and arranges the intensity of the aforesaid warning signal so as to be changed in response to the change in the measured value. Specifically, the present invention stepwise changes the intensity of a warning signal as the measured value approaches the upper limit or the lower limit of the standard temperature range.
A worker, therefore, receives feedback, before the upper limit or the lower limit of the standard temperature range has been reached, on the information that the upper limit or the lower limit is being approached, and that it is going to be soon reached. As a result, the work heating temperature can be always maintained at the predetermined standard temperature range. This permits the prevention of the occurrence of defective articles due to an excess, a shortage, or variations of the flame hardening temperature, which leads to the achievement of an improvement in the quality of product. Also, this permits even an unskilled worker to perform a high-accuracy flame hardening operation, which results in a significant effect on the rationalization and the labor-saving in the flame hardening process.
Recording measured values with recording means allows to work results of flame hardening to be outputted in the form of temperature graphs or numeral value lists, which also serves to the improvement in quality control function. Furthermore, recording measured values allows the changes in the flame hardening temperature with time to be left as records, which facilitates process management and the tracing and investigation of the cause of the occurrence of defective articles.
The apparatus for monitoring a work heating temperature in flame hardening in accordance with the present invention comprises a torch for use in flame hardening; a temperature sensor for measuring the temperature in the vicinity of the heated point on the work surface on the moving locus of the flame poured from the torch; controlling means connected to said temperature sensor, for comparing the measured value of temperature with a predetermined standard temperature range, and producing a warning signal when the measured value approaches the upper limit or the lower limit of the standard temperature range; and warning means operating in response to the signal from the aforesaid controlling means.
The aforesaid controlling means sends a warning signal to the warning means before the measured value reaches the upper limit or the lower limit of the standard temperature range, and changes the outputs of the warning means in response to the change in the aforesaid measured value. Also, the controlling means is arranged so that a physical quantity which appeals to the perception of a worker occurs by the operation of the warning means, and that the aforesaid physical quantity is stepwise changed as the measured value approaches the upper limit or the lower limit of the standard temperature range.
As a temperature sensor, various types of non-contact temperature sensors may be used. One example among them is an infrared temperature sensor. In this case, a sensor head is installed at a part of the torch, and connected to the controlling means via a flexible optical fiber.
In order to record a measured value, recording means is connected to the aforesaid controlling means. As recording means, magnetic recording means such as tape, card, or disk can be used, beside a pen recorder or a printer used to record the measured value on paper.
Hereinbelow, embodiments of the present invention will be explained with reference to the accompanying drawings.